1. Field of the Invention
The present invention relates to synthetic stucco facings for buildings and more particularly to synthetic stucco facings applied to cementitious wallboards coated with flexible resin.
2. Description of the Prior Art
Food and shelter have always been the two most primal needs of mankind and both have undergone a great deal of change since the dawn of our species. Shelter in particular has come a long way from the spelunking days of the caveman and has run the gamut from straw huts to stone temples and practically every other possibility in between. The design and construction of commercial and residential buildings have been the subject of much change especially in the past few decades with the advent of a bewildering array of new materials and methods. One of the most popular and widespread innovations of the century is the use of stucco facing on exterior building walls. A stucco facing consists essentially of a mixture of Portland cement, sand and sometimes small quantities of lime, applied in a plastic state to form a hard covering for exterior walls. The finish texture of stucco is usually rough and is controlled by the particle size of the mixture components.
The popularity of stucco is easily understood when considered in light of its low material, application and maintenance costs, pleasing esthetic qualities, and enhanced thermal insulation. Furthermore, because stucco is applied in a plastic state, it can conform to practically any shape. For this very same reason, stucco can be mixed in almost any color and can be finished in a variety of patterns, such as brick face or stone. Stucco is environmentally safe and easily lends itself to use by homeowners and other non-professionals.
However, stucco suffers from a number of very serious shortcomings. Because stucco is made up almost exclusively of sand and cement, it is porous and quite previous to moisture. When used in areas with high rain fall, stucco can lead to severe structural damage due to fungus and mildew formation when the underlying substrate is plywood or a similar material and can cause damage to interior walls when the underlying substrate is a water permeable material such as dry wall. Such damage remains unseen underneath the stucco facing and can go unchecked for many years, thereby gravely compounding the problem. To combat this shortcoming of conventional stucco, moisture barriers have been employed between the stucco facing and the underlying substrate. Wile their overall performance has been adequate, moisture barriers have typically given rise to their own problems, most significantly that of achieving adequate bonding of the stucco to the underlying substrate through the moisture barrier. Solutions devised to correct this problem have been cumbersome and expensive and typically involved the use of a metal mesh nailed to the substrate through the moisture barrier and holding in place an undercoating of stucco physically bonded to the mesh upon which the final exterior stucco facing is applied. This arrangement is complicated, expensive and time consuming to implement. Driving nails through the moisture barrier compromises the integrity of the barrier and thus defeats its very purpose. The metal mesh is relatively expensive and adds substantially to the weight that the walls must support. In addition, the combination of the mesh and the stucco must have substantial integrity independent of the substrate and the stucco facing is accordingly required to be fairly thick, further driving up weight and cost.
Because layers of stucco are water permeable, they seal against permeation of water to serve in preventing entry of water to be trapped against the underlying substrate and providing for free drainage of any such water that might enter from, for instance, imperfect seals at the peripheral edges of outside wallboard panels. It is obviously preferable to allow water to drain freely and thus special precautions must be taken along openings in the wall such as doors and windows to ensure that water is not absorbed by the wall panels before it has a chance to drain out. Such precautions usually include additional water barriers or flashing, all of which add to the cost and the complexity of the finished structure and thereby detract from the simplicity that is one of the most attractive attributes of stucco. Failure to properly address these shortcomings can result in serious problems for the unsuspecting homeowner, such as wood rot and interior leaks, in as little as two or three years after installation. For these very same reasons, stucco is obviously not well suited to use as roofing material, thereby significantly limiting its potential uses.
Stucco is also a very stiff covering and offers only mediocre impact resistance. Abrasion resistance is also quite poor and stucco covering can be scraped off by almost any hand wielded implement. Rigidity is an especially undesirable characteristic when combined with moisture permeability and, for this reason, stucco has a limited life span when exposed to repeated freeze/thaw cycles because the water absorbed expands and contracts as it freezes and thaws and thus creates internal fractures in the stucco facing that grow and allow even more water to infiltrate through to the underlying substrate. Stucco is therefore also not well suited for use in areas subject to freezing temperatures. Although this problem can be combated, it usually entails applying water sealing agents to the outer surface of the stucco finish. This is a costly approach that is not guaranteed to work because all exposed stucco must be fully saturated and because the sealing agents are usually susceptible to UV light, salt spray and chemicals. Such an approach is also likely to alter the color of the stucco, which is certainly a very undesirable side effect.
The rigidity of stucco also compromises its ability to maintain an attractive exterior surface with the passage of time. It is well known that wall panels tend to shift during the life of the building due to settling and seasonal variations in temperature and the joints between the panels must therefore accommodate these movements. The traditional solution to this problem is to fill the joint with a caulking compound. However, both hard and soft curing caulking compounds tend to shrink or expand under these circumstances and cannot be depended upon to maintain the water tight seal they were intended to form. In addition, both types of caulk give rise to irregularities on the outer surface of the stucco coat around the joint areas such as cusps or depressions that significantly and permanently alter the outward appearance of the stucco finish. Another well known problem is the formation upon curing of a discontinuity in appearance of the stucco coat across the face of the finished wall. This problem exhibits itself both across the face of individual wallboard panels and at the joint between juxtaposed panels.
One solution proposed entails applying a tape over the caulked joints, thus providing a flat surface that is more likely to accommodate the movements of the underlying wall panels and not disturb the overlying materials. Such tapes, however, require a bedding layer in order to adhere to the two adjoining panels, and can sometimes themselves create unsightly bulges on the outer surface of the stucco coat. In addition, joint sealing tapes are typically water proof and do not absorb water from the stucco mix, leading to the surface deformation problems described above.
Stucco is, nevertheless, a very popular construction material and various solutions have been posited for dealing with its shortcomings. It has been proposed, for example, that the wall panels be impregnated with a layer of epoxy upon which a layer of sand can be applied, thereby forming a water resistant layer that offers excellent bonding properties with the stucco mix. While certainly workable, this approach does not eliminate the need for additional coats between the stucco and the underlying substrate and thus is not a cost effective approach. In addition, the sand must be applied while the epoxy is still semi-fluid and therefore is likely to require professionally trained laborers utilizing professional and expensive equipment. Last but not least, applying sand to a wall is always a messy proposition that necessitates special precautions and/or costly cleanups.
Another approach calls for the application of an insulation layer upon the wall, followed by a vapor barrier applied as water-based liquid latex or paste, then covered by two coats of stucco. Various types of reinforcing meshes and bonding adhesives are also suggested as cures for any practical shortcomings this particular invention may exhibit. Although the use of a synthetic stucco mix comprising an acrylic based latex polymer is enumerated, the total number of layers for the finished wall has now increased to four with a corresponding increase in cost and complexity. While this approach is probably very successful for fluid storage structures for which it is intended, it is certainly not the simple, elegant, cost effective solution desperately needed by homeowners and real estate developers alike.
Yet another proposed solution separates the exterior coating from the underlying wall panels in the vicinity of the panel joints, thereby theoretically insulating the exterior covering from the underlying joint movements and the displacement of the caulking compound filing the joint. This is a partial solution because it only addresses the problem of joint displacement and the attendant marring of the exterior surface. This approach also overlooks the fact that as long as the stucco layer is bonded to wall panels that move, the stucco layer will be forced to move as well, often resulting in partial separation from the underlying substrate since it is not allowed to float above unaffected by the movements of the wall panels. For this reason, this approach is likely to have very limited application restricted solely to structures where wall panels do not move appreciably, and such structures are few indeed. Furthermore, this approach does not eliminate the need for installing water resistant layers but, rather, adds at least one additional layer that is installed along the panel joints to separate the stucco layer from the panel edges.
The assignee of the rights in the instant application introduced a composite wallboard construction having the adjoining edges taped to control the rate of cure of a synthetic stucco applied thereto. This construction is shown in my U.S. Pat. No. 5,732,250. While satisfying a long felt commercial need, this construction suffers the shortcoming that commercial grade wallboards typically absorb moisture at different rates across the surfaces thereof. This causes the stucco applied to, in some instances, cure at different rates across the surface thus resulting in an uneven finished surface.
New housing is being erected throughout the civilized world at an accelerating rate and the level of comfort and durability demanded of such structures is increasing as well. What is urgently needed is an attractive exterior wall which exhibits an even finished appearance but is low cost, adaptable and easy to install while offering much improved moisture protection, impact and abrasion resistance, and resistance to freeze/thaw cycles.
The method of the present invention is characterized by an exterior synthetic stucco wall construction wherein commercial grade cementitious wallboard panels are selected having an exterior surface covered by a coating which will provide for uniform moisture absorption across the face of such panels and selecting an elastomeric adhesive joint sealing tape for covering gaps formed between adjacent edges of such panels to cooperate in affording overall uniform moisture absorption. Synthetic stucco mix of the type including components of water based resinous latex, coalescing agents, dispersants, defoamers, surfactants and inert fillers is mixed with such components in a ratio to, when applied over such coating and tape, cure and provide a strong bond and exhibit flexibility, water resistance, and substantially uniform exterior coloration across the face of the exterior wall formed by the wallboard panels.
The present invention takes advantage of commercial grade cementitious fiber wallboard panels that are free of asbestos and other inorganic fibers and are environmentally safe to install. The cementitious wallboard panels provide an excellent bonding surface for a uniform acrylic or other synthetic resin coating to provide for uniform absorption from a synthetic stucco mix applied thereover. The panels are installed on wood or metal frame structures with small gaps between the panels. Polyurethane caulk is applied to the gaps between the panels and allowed to cure. Polyurethane caulk remains flexible once it has cured and usually maintains, although not always, its integrity when the wall panels settle or move due to seasonal temperature variations. The elastomeric adhesive joint sealing tape applied over adjoining edges of panels to cover all gaps and to comers has a thin fabric backing that allows minimal amounts of water to be absorbed from the synthetic stucco layer. The elastomeric adhesive on the tape provides a water tight seal along the joints and ensures that any water that permeates the synthetic stucco layer does not infiltrate through the joints to the interior walls of the building. The tape and coating cooperate to provide for a relatively uniform rate of moisture absorption to thus provide for a substantially uniform cure rate for such stucco across the entire face of the wall formed by the wallboard panels.
The synthetic stucco mixture may be applied by trowel or sprayer on the outer surface of the coated panels and over the tape on the joints and can be finished to the desired texture. Such stucco mixture is of a generally uniform thickness and porosity and the coating and tape of comparable absorption rates so that the curing rate across the surface of the wall formed by the combined panels is controlled to be substantially uniform to thus prevent formation of irregularities in the surface of such stucco as might otherwise occur from uneven curing. The fabric backing of the sealing tape provides a flat porous surface that the overlying synthetic stucco coat bonds and adheres to regardless of any movement or settling of the underlying panels and caulk. Because the tape has a very low profile, the synthetic stucco coating does not xe2x80x98ride upxe2x80x99 and bulge over the tape even when the coating is very thin and there is no need for applying the traditional bedding coat to disguise the presence of the tape. The synthetic stucco mixture cures as water evaporates from it or is absorbed through the coating on the underlying wall panels and the fabric backing of the adhesive tape. Because the fabric backing of the tape also absorbs water from the synthetic stucco mixture, it cooperates with the coating to prevent non-uniform appearance in the outer surface of the synthetic stucco coat in the vicinity of the panel joints due to unequal water absorption.
The synthetic stucco mixture is preferably an acrylic or other compatible water based resinous latex emulsion containing calcium carbonate or other non-reactive sand. The mixture bonds extremely well to the coating on the wall panels and to the fabric backing of the elastomeric sealing tape. In addition, the latex in the mixture provides an effective barrier against water infiltration and remains flexible when cured to thus offer significantly improved abrasion and impact resistance while being highly resistant to damage from repeated freeze/thaw cycles and unaffected by most chemicals. The present invention therefore provides a method for producing a synthetic stucco finished exterior wall with a single coat application of synthetic stucco mix and extends the range of projects that can now employ a stucco-like material and reap its traditional advantages as well as the new benefits disclosed herein.
Furthermore, the latex employed is water based and the mixture is environmentally safe to apply. In addition, latex emulsions are compatible with a wide range of coloring agents and the synthetic stucco finish can therefore be manufactured and applied in virtually any color desired.
The wall apparatus of the present invention is characterized by wallboard panels, each covered by a coating, having a predetermined moisture absorption characteristic to cooperate with a joint sealing tape having a selected moisture absorption characteristic so a water based synthetic stucco applied evenly across the face thereof will cure at the same rate throughout the wall area to afford a uniform exterior surface.
Other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the features of the invention.